Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations cover the safety profile (non-read-only, non-idempotent, non-destructive), and the description adds substantial behavior beyond that: the exact retry schedule, which HTTP statuses trigger retries and which do not, the auth requirement, the HMAC header and attempt header, the payload type and fields, and the failure codes. This is unusually rich disclosure for a mutation tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the operation and the key precondition, and every sentence carries operational information. It is on the long side and repeats the POST/signed-JSON idea and the error-code list slightly, but no sentence is filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description carries the return contract itself: success shape (ok, delivery, errors) and failure codes (not_found, not_completed, no_webhook, webhook_not_enabled), plus the explicit note that it does not mint a new login link. Nothing needed to call it correctly is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% for the single parameter, so the baseline is high. The description still adds value by mapping the caller-side name ('Pass the sessionId from create_login_link as session_id') and restating the completion/webhook-URL precondition that governs valid input.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Send the signed login webhook again') and immediately scopes it to sessions that already used the webhook method, which cleanly separates it from create_login_link and get_login_status. An agent can identify the tool's job without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit preconditions ('session must be completed or consumed', must include a webhook URL) and explicitly rules out the 'prior delivery failure required' assumption. It also names the exclusions ('Redirect, post_message, and form_post do not use this tool') and points at create_login_link as the source of the session, so when/when-not is fully covered.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.